Fluid level sensor

ABSTRACT

A fluid sensor system capable of sensing a fluid level or a volume of fluid held by a reservoir, such as a container or a tank. In one embodiment, the system may include a magnetic element in a flotation device that suspends the magnetic element in the fluid held by the reservoir, so that the magnetic element randomly floats in proximity to a top of the fluid surface. Two or more magnetic field sensors or magnetometers are associated with the reservoir in at least two different locations, spaced apart from one another. The system further includes a processor coupled to the sensors. The magnetic field sensors may sense the strength of the magnetic field around the magnetic element to generate signals that are sent to the processor. The processor may then determine the location of the magnetic element within the reservoir based on the signals. The determined location can be correlated to a volume of fluid within the tank which is output to another device and/or a user.

TECHNICAL FIELD

The present application relates to a fluid level sensor, and moreparticularly to a field-based fluid level sensor system.

BACKGROUND

Fluid level sensors are used in a variety of applications that involvedetecting a level of fluid within a container. One application ofgrowing significance is in the field of fuel senders for fuel tanks invehicles. In a conventional arrangement, a fuel sender, more generallyknown as a type of fluid level sensor, can be disposed within a fueltank, and may include a float that is mechanically coupled to a mainbody of the sender unit and that rises and falls along with the fuellevel in the container. The float may be rotatably coupled to the mainbody via a float arm whose angular position corresponds to the floatposition and therefore the fluid level in the container. Conventionally,an electrical or actively powered sensor is placed within the containeras part of the fuel sender and along with the float to sense the angularposition of the float arm. Examples of such active sensors includerheostat sensors and inductive-based sensors. Such a sensor isconventionally powered via wiring or an electrical connection, or both,by a power supply external to the container. As a result, installationand use of the fuel sender involves providing power to components (e.g.,the electronic sensor) within the container. Further, installation anduse of the fuel sender also involves disposing mechanical as well aselectrical components within the container, thereby increasing thecomplexity of installation and any potential repair efforts.

Incorporation of electrical components and providing power thereto intoa container can present several design considerations. Conventionally,if the fluid being stored in the container is corrosive or generallyreactive, the fuel sender is constructed such that the electricalcomponents and associated electrical conductors are sealed from thefluid by non-reactive materials. Such a construction, including use ofsuch non-reactive materials, can increase the cost and complexity of thefuel sender.

Another design consideration with respect to use of electricalcomponents within a fluid container includes limiting or constrainingthe voltage or current, or both, supplied to the electrical components.In this way, the power supply may be limited to substantially avoidignition of potentially flammable vapor within the container. Componentselection of the fuel sender is often driven by these considerations.

SUMMARY OF THE DESCRIPTION

The current embodiments provide a fluid sensor system capable of sensinga fluid level or a volume of fluid held by a reservoir, such as acontainer or a tank.

In one embodiment, the system may include a magnetic element having aflotation device that suspends the magnetic element in the fluid held bythe reservoir, so that the magnetic element randomly floats in proximityto a top of the fluid surface. Two or more magnetic field sensors,optionally magnetometers, are associated with the reservoir in at leasttwo different locations, spaced apart from one another. The systemfurther includes a processor coupled to the sensors. The magnetic fieldsensors may sense the strength of the magnetic field around the magneticelement to generate signals that are sent to the processor. Theprocessor may then determine the location of the magnetic element withinthe reservoir based on the signals. The determined location can becorrelated to a volume of fluid within the tank which is output toanother device and/or a user.

In another embodiment, the processor may triangulate the location orposition of the magnetic element within the reservoir based on one ormore signals sensed by one or more magnetic field sensors. The magneticfield strength in proximity to each of the one or more magnetic fieldsensors may vary based on the distance between each respective magneticfield sensor and the magnetic element. The processor may be coupled tomemory that stores instructions relating to a functional relationshipbetween the magnetic field strength sensed by the one or more magneticfield sensors and fluid level or volume of fluid held by the reservoir.The functional relationship may account for variations in movement ofthe flotation device on or adjacent a surface of the fluid so that suchmovement does not affect a determined fluid level based on the sensedmagnetic field strengths. As an example, the processor may be determinethe location of the flotation device by calculating angles, based onoutput from the one or more magnetic field sensors, relative to knownlocations of the one or more magnetic field sensors. The calculatedangles may be relative to a fixed baseline defined by the knownlocations of the one or more magnetic field sensors. As another example,in an embodiment having three magnetic field sensors disposed at fixedpositions, the processor may triangulate the position of the magneticelement as a function of variances in the sensed strength of themagnetic field emanating from the magnetic element.

In yet another embodiment, the system may include a flotation devicejoined with a magnetic element and that floats in proximity to a surfaceof the fluid held by a fluid reservoir. One or more magnetic fieldsensors may be disposed on or in proximity to a wall of the fluidreservoir, and may provide sensor output indicative of a magnetic fieldstrength. The magnetic field strength may vary as a function of theposition of the magnetic element with respect to the one or moremagnetic field sensors. As an example, the one or more magnetic fieldsensors may include a plurality of magnetic field sensors disposed atdifferent positions, and the magnetic field strength sensed by each onthe magnetic field sensors may be different depending on the relativedistance from the magnetic element.

In still another embodiment, movement of the flotation device may besubstantially constrained to a single axis of travel by a flotationguide, such a rod or tube.

In even another embodiment, movement of the filtration device may besubstantially random about the surface of the fluid held by the fluidreservoir.

In a further embodiment, the one or more magnetic field sensors may bedisposed at various locations, including internally or externally, or acombination thereof, with respect to the fluid reservoir. As an example,the one or more magnetic field sensors may be disposed outside the fluidreservoir and the flotation device may be disposed inside the fluidreservoir, thereby avoiding placing electric circuitry of the sensorsystem within the fluid reservoir. Further, the magnetic field sensorsmay be disposed on a wall of the fluid reservoir or adjacent thereto.

In yet a further embodiment, the flotation device including the magneticelement may be constructed such that the flotation device self-orientswhile floating. For instance, the flotation device may be weighted suchthat, in floating in proximity to a surface of the fluid, the flotationdevice rights itself to substantially maintain a particular orientationwith respect to a surface of the Earth or the gravitational accelerationvector of the Earth. As another example, the flotation device may beconstructed to include a greater amount of buoyant compositiondistributed away from a center of mass of the flotation device so thatthe flotation device orients itself with respect to the surface of thefluid.

In still another embodiment, a method of determining a fluid level offluid held by a fluid reservoir includes floating a magnetic element inproximity to the surface of the fluid. In one embodiment, the magneticelement may randomly float with respect to the surface. In anotherembodiment, the magnetic element may be constrained to movement along asingle axis of travel.

The method according to this embodiment may include sensing first andsecond magnetic field strengths from respective first and secondmagnetic field sensors that are disposed at different positions. Thefirst and second magnetic field strengths may respectively vary orchange based on a relative position between the magnetic element and thefirst and second magnetic field sensors. Based on the sensed first andsecond magnetic field strengths, a position of the magnetic element maybe determined and correlated to a fluid level of the fluid held by thefluid reservoir. Optionally, the fluid level of the fluid may bedetermined directly from the sensed first and second magnetic fieldstrengths.

In even a further embodiment, a fluid level sensor system may determinea fluid level of fluid held by a reservoir based on information relatingto sensed magnetic field strength from one or more locations. The sensedmagnetic field strength may be different at each location and may varybased on a relative position or distance between each location and amagnetic element. The magnetic element may be coupled to a flotationdevice that floats the magnetic element in proximity to a surface of thefluid. With this configuration, the fluid level sensor system accordingto one embodiment may determine a fluid level without disposingcircuitry or other electrical components into the fluid reservoir or incontact with the fluid. Further, in one embodiment, installation andoperation of the fluid level sensor system can be simpler thanconventional systems in that the flotation device can be dropped intothe reservoir and can randomly float toward areas not readily accessiblefor measurement by conventional systems. For instance, the fluid levelsensor system according to one embodiment can be configured to sensefluid level within differently shaped reservoirs, including reservoirshaving narrow passages or volumes that conventional float arm-based fuelsenders do not operate within. These and other advantages and featuresof the invention will be more fully understood and appreciated byreference to the description of the current embodiment and the drawings.

Before the embodiments of the invention are explained in detail, it isto be understood that the invention is not limited to the details ofoperation or to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention may be implemented in various other embodimentsand of being practiced or being carried out in alternative ways notexpressly disclosed herein. Also, it is to be understood that thephraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including” and “comprising” and variations thereof is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items and equivalents thereof. Further, enumeration may beused in the description of various embodiments. Unless otherwiseexpressly stated, the use of enumeration should not be construed aslimiting the invention to any specific order or number of components.Nor should the use of enumeration be construed as excluding from thescope of the invention any additional steps or components that might becombined with or into the enumerated steps or components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a field-based fluid level sensor system according to afirst embodiment associated with a fluid container.

FIG. 2 depicts a representative view of the fluid level sensor systemaccording to the first embodiment.

FIG. 3 shows a representative graph of the functional relationshipbetween magnetic field strength and a level of fluid in the fluidcontainer according to the first embodiment.

FIG. 4 shows a field-based fluid level sensor system according to asecond embodiment arranged conjunction with the fluid container.

FIG. 5 shows a representative graph of the functional relationshipbetween magnetic field strength and a level of fluid in the containeraccording to the second embodiment.

FIG. 6 shows a magnetic float according to the first embodiment.

FIG. 7 shows a magnetic flow according to a third embodiment.

FIG. 8 shows a magnetic flow according to a fourth embodiment.

DESCRIPTION

A fluid level sensor system in accordance with one or more embodimentsof the present disclosure is shown in FIG. 1, and generally designated100. As set forth below, the fluid level sensor system 100 may include aflotation device 102 adapted to float within a container 10. Theflotation device 102 is configured such that it is buoyant relative to afluid 12 held by the container 10, thereby rising and falling with asurface of the fluid 12 being held by the container 10. In other words,the position of the flotation device 102 may be indicative of a fluidlevel of the fluid 12 being held by the container 10. The fluid levelsensor system 100 may be configured to detect one or more positionalparameters of the flotation device 102 relative to one or moremagnetometer sensors 110, 112, and to determine a fluid level of thefluid 12 based on the one or more positional parameters. The positionalparameters in one embodiment may include a precise spatial location of amagnetic element coupled to the flotation device 102.

The container 10 may be any type of tank or reservoir for holding fluid12, including for example a fuel tank. Further, the container 10 may besealed in some applications, and unsealed or open in other applications.

For purposes of disclosure, the fluid 12 within the container 10 isdescribed at portions herein as being fuel within a fuel tank, but itshould be understood that the present disclosure is not so limited andthat any type of fluid may be held by the container 10 and that thefluid level sensor system 100 may be adapted to determine a fluid levelof any fluid held by the container 10. Example applications include butare not limited to septic tanks, food processing tanks, farm ponds,sewer or water treatment plants, oil refineries, oil tank, cargocontainers, ship holds, grill propane tanks, rural propane tanks,clinical tanks, chemical tanks, any liquid storage tank, ballasts forwatercraft. Additional example applications include fat sacks (forboats), or any other type of dynamic tank or reservoir that can changein size or shape, or both. Further example applications include aviationfuel tanks at any location on the air craft, toilet bowl reservoirs,windshield fluid tanks, hot water tanks, water holding tanks (e.g., rooftops, natural rain water), coffee makers, portable restroom reservoirs,hazardous tanks, liquefied natural gas (LNG) tanks, liquid nitrogenstorage, hydrogen storage, and urea storage.

The container 10 may be formed of any type of material, includingnonmagnetic material or magnetic material, or a combination thereof. Inprincipal, the material used for the container 10 may depend on the typeof fluid 12 to be held by the container 10. For example, if the fluid 12is a fuel that reacts to several types of materials, a non-reactivematerial with respect to the fluid 12 may be used for the container 10.In one embodiment, the container 10 may be formed primarily ofnonmagnetic, plastic material such as polyethylene. The container 10 maybe a substantially rigid such that the container substantially maintainsits shape regardless of the amount of fluid being held. Alternatively,the container 10 may be soft such that the container 10 can expand orchange shape, or both. For instance, the soft structure of the container10 may enable expansion thereof such that an internal volume of thecontainer 10 can increase to accommodate additional fluid.

The fluid level sensor system 100 according to one embodiment may be afuel sender for use in conjunction with a vehicle. In this context, thefluid level sensor system 100 may provide a fuel sender output, such asan analog voltage output or a variable resistance output, that isindicative of a fluid level of the fluid 12 held by the container 10.This fuel sender output may be fed or provided to components of thevehicle, such as a fuel gauge.

For example, the fuel sender output of the fluid level sensor system 100may have a resistance in a range of 240-30 ohms, where 240 ohmscorresponds to an empty container and 30 ohms corresponds to a fullcontainer. The fuel gauge may be configured to indicate the fluid levelbased on the resistance of the fuel sender output. As fuel is consumedfrom the fuel tank by the vehicle engine, there is a decrease in heightof the fluid 12 and the flotation device 102 relative to a bottom of thefuel tank. The fluid level sensor system 100 may be configured todetermine a height of the flotation device 102 based on magnetic sensoroutput from the one or more magnetometers 110, 112, to determine a fluidlevel based on the determined height, and to vary the fuel sender outputto correspond to the determined fluid level. In this example, as thefuel is consumed by the vehicle engine, the resistance of the fuelsender output increases. It should be understood that the fluid levelsensor system 100 may provide any type of output indicative of a fluidlevel of fluid 12 held by the container 10, and that the presentdisclosure is not limited to any particular feature or aspect of thedescribed example.

The flotation device 102 in the illustrated embodiment of FIG. 1 mayinclude a magnetic element, such as a permanent magnet or magneticmaterial, such as ferromagnetic or paramagnetic material. One example ofa magnetic material is iron, but any type of magnetic material may beused. In the illustrated embodiment, the magnetic element 108, itself,may not be buoyant relative to the fluid 12—however, the flotationdevice 102 may include a buoyant composition 109 that can overcome theweight of the magnetic element 108 such that the flotation device 102,including the magnetic element 108 and the buoyant composition 109, maybe buoyant relative to the fluid 12.

An example of such a flotation device 102 is shown in a sectional viewin the illustrated embodiment of FIG. 6. The flotation device 102 in theillustrated embodiment includes a magnetic element 108 and buoyantcomposition 109 that is arranged to hold the magnetic element 108. Thebuoyant composition 109 may encapsulate the magnetic element 108 asshown in the illustrated embodiment—but it should be understood thatencapsulation is not a necessity. For example, rather than beingencapsulated within the buoyant composition 109, the magnetic element108 may be disposed on the buoyant composition 109. The buoyantcomposition 109 may include one or more voids to which a surface thereofmay be joined with the magnetic element 108. Adhesive or a mechanicalinterlock, or any type of joining or fastening mechanism may be used tojoin the magnetic element 108 and the buoyant composition 109.

Optionally, the magnetic element 108 may not be joined with the buoyantcomposition 109—instead, the magnetic element 108 may be held within orconstrained by the buoyant composition 109. For instance, the magneticelement 108 may be constrained within a void of the buoyant composition109 such that the magnetic element 108 can freely move within the void.For example, the buoyant composition 109 may include a sealed, plasticshell that is filled with an inert gas and contains the magnetic element108. In this way, the magnetic element 108 can freely move within theplastic shell, but because the density of the magnetic element 108 isgreater than the inert gas, the magnetic element 108 may orient itselfwithin the plastic shell such that the magnetic element 108 acceleratesor lies along the gravitational acceleration vector of the Earth.

In the illustrated embodiment, the magnetic element 108 may be disposedoff center relative to a central axis 132 of the flotation device 102 sothat the weight or density distribution of the flotation device 102 isasymmetrical. In this way, the flotation device 102 may beself-orienting. As can be seen in the illustrated embodiment of FIG. 6,the magnetic element 108 includes North and South poles (N-S). Becausethe flotation device 102 is configured to self-orient on the surface ofthe fluid 12, the magnetic element 108 may be disposed such that the N-Spoles are aligned normal or perpendicular to a surface of the fluid 12.

In the illustrated embodiment, the buoyant composition 109 may be anon-reactive composition that does not react to the fluid 12 held by thecontainer 10, and may be less dense than the fluid 12 such that theflotation device 102 floats in proximity to a surface of the fluid 12.The buoyant composition 109 may be comprised of a plurality ofcompositions that together achieve buoyancy of the flotation device 102relative to the fluid 12. As an example, the buoyant composition 109 mayinclude plastic having one or more voids that are filled with anothercomposition, such as a gas. Examples of gases that may facilitatebuoyancy include air, nitrogen, or inert gas.

The flotation device 102 may be sized and configured so that it can beeasily installed within the container 10. In one embodiment, theflotation device 102 may be “dropped” or otherwise disposed in thecontainer 10 through an opening of the container 10 (e.g., the fillopening) during manufacture. In an alternative embodiment, the flotationdevice 102 may be larger than a fill opening of the container 10, butmay be disposed within the container 10 at manufacture by placing theflotation device 102 in the container 10 during formation of thecontainer 10 and prior to one or more openings of the container 10 beingtoo small or sealed to prevent placement of the flotation device 102.With this configuration, it may not be possible to remove the flotationdevice 102 from the container 10 without disassembling the container 10.In one embodiment, during manufacture of the container 10, the flotationdevice 102 may be installed within the container 10 and adhered to aninner wall of the container 10 using a fluid dissolvable adhesive. Thisway, the adhesive may prevent the flotation device 102 from freelymoving within the container 10 during shipment and prior to thecontainer 10 being filled with the fluid 12.

The fluid level sensor system 100 may include one or more magnetic fieldsensors 110, 112, such as magnetometer sensors as mentioned herein. Inthe illustrated embodiment of FIG. 1, the one or more magnetic fieldsensors include a first magnetic field sensor 110 and a second magneticfield sensor 112. The one or more magnetic field sensors 110, 112 may beany type of magnetic field sensor capable of sensing a magnetic fieldstrength (e.g., a Gauss value) along one or more axes or varying anoutput based on strength of the magnetic field. In the illustratedembodiment, the one or more magnetic field sensors 110, 112 may be3-axis magnetometers configured to sense a magnetic field strength along3-orthogonal axes (X, Y, and Z), and may utilize a magneto resistivetype sensor formed as an integrated circuit. The type of magnetic fieldsensor 110, 112 is not limited to a magnetic resistive type sensor. Anytype of magnetic field sensor may be utilized, including, for example, amagnetic inductive sensor. The one or more magnetic field sensors 110,112 may be disposed on or in proximity to a container wall of thecontainer 10. Further, the one or more magnetic field sensors 110, 112may be positioned inside the container 10 or outside the container 10,or a combination thereof.

A variety of factors may affect the sensed magnetic field strength,including the strength of the Earth's magnetic field at a particularlatitude and longitude, deviations in the Earth's magnetic fieldpotentially due to proximity to a ferromagnetic or magnetic material,and a position of the flotation device 102 relative to the magnetometer.The one or more magnetic field sensors 110, 112 may provide one or moreoutputs indicative of the magnetic field strength along the one or moreaxes. As an example, the one or more magnetic field sensors 110, 112 mayprovide a digital communication interface, such as an I2C interface,through which a separate controller or sensor circuitry 120 can obtaindigital information relating to a magnetic field strength along the oneor more axes. As another example, the one or more magnetic field sensors110, 112 may provide one or more analog outputs whose output voltagerange corresponds to a range of magnetic field strength. The one or moreanalog outputs can be sensed and converted via an analog-to-digitalconverter to a digital value representative of the magnetic fieldstrength.

The fluid level sensor system 100 as described herein may include sensorcircuitry 120 operably coupled to the one or more magnetic field sensors110, 112 to obtain sensor information relating to a magnetic fieldstrength along one or more axes. The sensor circuitry 120 may include acontroller or microprocessor and memory with instructions to direct themicroprocessor to calculate a fluid level based on the sensorinformation obtained from the one or more magnetometer sensors 110, 112.

In one embodiment, because the flotation device 102 includes a magneticmaterial 109, a strength of the magnetic field sensed by the one or moremagnetic field sensors 110, 112 may change as the flotation device 102moves relative to the one or more magnetic field sensors 110, 112. Inother words, a magnetic field strength along one or more axes sensed bythe first magnetic field sensor 110 may depend on a position of theflotation device 102 relative to the first magnetic field sensor 110.Likewise, a magnetic field strength along one or more axes sensed by thesecond magnetic field sensor 112 may depend on a position of theflotation device 102 relative to the second magnetic field sensor 112.The sensor circuitry 120 may obtain sensed information from the firstand second magnetic field sensors 110, 112 that relates to magneticfield strength sensed by the respective magnetic field sensor, anddetermine a fluid level of the fluid 12 held by the container 10 basedon the sensed information.

In the illustrated embodiment, a plurality of magnetic field sensors110, 112 may be disposed on or in proximity to the container 10 atdifferent positions. For instance, the first magnetic field sensor 110may be disposed near a full level, and the second magnetic field sensor112 may be disposed near an empty level of the container 10. Because theflotation device 102 can float within the container 10 and rises andfalls with a fluid level of the fluid 12, and because the plurality ofmagnetic field sensors 110, 112 are disposed of different positions, amagnetic field strength sensed by one magnetic field sensor may bedifferent from a magnetic field strength sensed by another magneticfield sensor. The sensor circuitry 120 may analyze these differentsensed magnetic field strengths to determine a position of the flotationdevice 102 with respect to the plurality of magnetometer sensors 110,112. In one embodiment, the sensor circuitry 120 may utilizetriangulation techniques based on the relative strength of the sensedmagnetic fields to determine the position of the flotation device 102.

The sensor circuitry 120 in one embodiment may include a controller or amicroprocessor and memory that stores instructions to determine a fluidlevel of the fluid 12 held by the container 10 based on sensed magneticfield strength information. In one embodiment, as described above, thesensed magnetic field strength information may be obtained from aplurality of magnetic field sensors, each disposed at differentpositions, such that the relative sensed magnetic strength measured bythe plurality of magnetic field sensors is indicative of a position ofthe flotation device 102 within the container 10.

In the illustrated embodiment of FIGS. 2 and 3, functional relationshipsamong magnetic field strength, position of a magnetic field sensor, andposition of the flotation device 102 are shown in relation to a fluidlevel of fluid 12 held by the container 10. For purposes of disclosure,in the illustrated embodiment, the flotation device 102 includes apermanent magnet 108 that emanates a magnetic field B and is orientedwith its N-S poles aligned with the gravitational acceleration vector ofthe Earth, which is depicted as the Z-axis in FIG. 2. The level of thefluid 12 held by the container 10 also corresponds to a position alongthe Z-axis in FIG. 2. While floating on the surface of the fluid 12, theflotation device 102 can move freely in along the X and Y axes depictedin FIG. 2, and can rise and fall with the level of the fluid 12 alongthe Z-axis. It should be understood that the X, Y, and Z axes could beoriented differently, but have been chosen as shown in FIG. 2 tofacilitate discussion.

The magnetic field B emanating from the flotation device 102 may vary instrength as a function of distance. More specifically, the strength ofthe magnetic field B may be approximately 1/r³, where r is a distancefrom the flotation device 102. It should be understood there are severalother factors that can affect magnetic field strength at a measurementpoint or location relative to the flotation device 102, including, forexample, orientation of the magnetic element 108 (or its principal N-Svector) relative to a point of measurement that can affect a measuredstrength of the magnetic field B. The physical dimensions of themagnetic element 108 may also affect the measured strength of themagnetic field B at a measurement location or point. These factors amongothers can affect a measured strength of a magnetic field at a point orlocation relative to the magnetic element 108 of the flotation device102. However, for purposes of disclosure, the strength of the magneticfield can be approximated as 1/r³.

In the illustrated embodiment of FIGS. 2 and 3, the flotation device 102is depicted at a Z-axis position corresponding to a fluid level betweenfull (or 100% full) and half-full (or 50% full). The magnetic fieldsensors 110, 112 are disposed respectively near the full and emptypositions. As a result, as can be seen, a distance r2 between the firstmagnetic field sensor 110 and the flotation device 102 is smaller than adistance r2 between the second magnetic field 112 and the flotationdevice 102. The measured magnetic field strength B1 in proximity to thefirst magnetic field sensor 110 is therefore likely to be greater thanthe measured magnetic field strength B2 in proximity to the secondmagnetic field sensor 112. Based on the measured magnetic fieldstrengths B1, B2, the sensor circuitry 120 may calculate a fluid levelof the fluid 12 corresponding to the Z-axis position of the flotationdevice 102. More particularly, the sensor circuitry 120 may determinethe fluid level as a function of the measured magnetic field strengthsB1, B2 according to some function F. In one embodiment, the firstmagnetic field sensor 110 may be positioned at or near the full Z-axisposition, and the second magnetic field sensor 112 may be positioned ator near the empty Z-axis position. The sensor circuitry 120 maydetermine fluid level based on the difference between a) the sensedmagnetic field strength of the first magnetic field sensor 110 and b)the sensed magnetic field strength of the second magnetic field sensor112. The functional relationship between fluid level or Z-axis positionand the sensed magnetic field strengths may be linear and calculated,for example, based on the difference in sensed magnetic field strengthbetween the “empty” sensor and the “full” sensor. The Z-axis differencemay be factored out because the distance to three points are determinedor known: 1) the determined distance between the magnet and the emptysensor, 2) the determined distance between the magnet and the fullsensor and 3) the known distance between the empty sensor and the fullsensor.

In the illustrated embodiment, because the flotation device 102 isallowed to float along the surface of the fluid 12, the flotation device102 may move freely in an X-Y plane or along the X-axis and the Y-axis.This free movement may cause variations in the magnetic field strengthmeasured by the first and second magnetometers 110, 112. In other words,as the flotation device 12 floats freely in a direction toward or closerto the first magnetic field sensor 110, the measured magnetic fieldstrength B1 may increase. And, likewise, as the flotation device 102floats freely in a direction farther from the first magnetic fieldsensor 110, the measured magnetic field strength B1 may decrease. Thesame can be said for the measured magnetic field strength B2 sensed bythe second magnetic field sensor 112.

Although the flotation device 102 may move freely along the X and Yaxes, the Z-axis position of the flotation device 102 may besubstantially stable or constant (assuming no changes in actual fluidlevel and no changes in orientation of the container 10 relative to thegravitational acceleration vector of the Earth. In other words, theposition of the flotation device 12 corresponding to a fluid level maybe substantially constant in a stable environment. As mentioned herein,movement of the flotation device 12 in an X-Y plane or along the X and Yaxes may correspond to a change in the respective distances r1, r2between the first and second magnetometer sensors 110, 112 and theflotation device 12. However, in the illustrated embodiment, there is afunctional relationship between the distances r1, r2 and the Z-axisposition or a fluid level such that the sensor circuitry 120 candetermine a fluid level or Z-axis position based on an indication of thedistances r1, r2.

The respective distances r1, r2 between the one or more magnetometersensors 110, 112 and the flotation device 102 may not be directlymeasurable, but in the illustrated embodiment, information relating tothese distances may be determined based on the measured magnetic fieldstrengths B1, B2. Based on the measured magnetic field strengths B1, B2obtained from the one or more magnetic field sensors 110, 112, thesensor circuitry 120 may determine the fluid level or Z-axis position ofthe flotation device 102 in the container 10. The functionalrelationship between the measured magnetic field strength B1, B2 mayyield information relating to the distances r1, r2 and therefore theZ-axis position of flotation device 102.

In the illustrated embodiment of FIG. 3, a functional relationshipbetween the magnetic field strength B1, B2 and fluid level or Z-axisposition is shown. For purposes of disclosure, the functionalrelationship is depicted as being generally linear; however, it shouldbe understood that the functional relationship may not be linear. Forinstance, the functional relationship may be parabolic or exponential.It should also be understood that the functional aspects used todetermine the Z-axis position of the flotation device 102 may be basedon additional parameters, including measured parameters or predeterminedparameters or a combination thereof. In embodiments in which there aremore than two measured magnetic field strengths obtained from more thantwo magnetometer sensors, the functional relationship may be representedby a corresponding number of dimensions.

The Z-axis position of the flotation device 102, in the illustratedembodiment of FIG. 3, may functionally correspond to the ratio between(a) the magnetic field strength B1 measured by the first magnetic fieldsensor 110 and (b) the magnetic field strength B2 measured by the secondmagnetic field sensor 112. For instance, at the Z-axis positioncorresponding to Z_Actual, the ratio between the magnetic fieldstrengths B1, B2 may follow a linear relationship despite changes instrength due to position changes along the X axis and the Y axis, orboth. As the flotation device 102 moves farther away from both the firstand second magnetometer sensors 110, 112, the measured magnetic fieldstrengths B1, B2 may decrease in a corresponding manner—however, asshown in FIG. 3, the ratio between the measured magnetic field strengthsB1, B2 and the Z-axis position may follow a linear relationship alongthe line labeled Z_Actual. As a result, the sensor circuitry 120 mayobtain the measured magnetic field strength B1, B2 from the first andsecond magnetic field sensors 110, 112, and calculate the Z-axisposition or fluid level as a function of the measured magnetic fieldstrengths B1, B2. If the Z-axis position changes, similar functionalrelationships based on the measured magnetic field strengths B1, B2 maybe implemented to determine the Z-axis position change, including, forexample, those shown and labeled as Z_(100%), Z_(50%) and Z_(0%) in FIG.3.

In some applications, the container 10 may be in motion and may notremain static. Vehicle applications, such as cars or watersports, areexamples of such non-static applications. As a result, the fluid 12 heldby the container 10 may be in motion, and the float 12 may also be inmotion. This type of motion may be considered unrelated to the actualfluid level of the fluid 12 held by the container 10, but may affect orcause variations in the sensed magnetic field strength of the one ormore magnetic field sensors 110, 112. Filtering of the sensed magneticfield strength may be implemented to substantially remove or preventsensor variations unrelated to changes in the fluid level from affectingthe determined fluid level of the fluid level sensor system 100. Kulmanfiltering is one example of a filter technique that may be inconjunction with preventing unrelated motion from affecting thecalculated fluid level.

A fluid level sensor system in accordance with one embodiment of thepresent disclosure is shown in FIG. 4, and generally designated 200. Thefluid level sensor system 200 may be similar to the fluid level sensorsystem 100 described herein, but with several exceptions. For example,the fluid level sensor system 200 may include a flotation device 202, amagnetic field sensor 210, and sensor circuitry 220 similar in somerespects to the flotation device 102, the one or more magnetic fieldsensors 110, 112, and the sensor circuitry 120 described in connectionwith the fluid level sensor system 100. In the illustrated embodiment,the fluid level sensor system 200 may be configured such that theflotation device 202 is constrained by a flotation guide 204 to travelsubstantially along a single axis. A position of the flotation device202 along this single axis may correspond to a fluid level of the fluid12 held by the container 10.

The single axis of travel in the illustrated embodiment of FIG. 4 may bealigned with a longitudinal axis of the flotation guide 204, along whichthe flotation device 202 may travel. In the illustrated embodiment, theflotation guide 204 may be in the form of a rod or tube disposed throughan aperture of the flotation device 202. This rod configuration of theflotation guide 202 may enable the flotation device 202 to freely movealong the longitudinal axis of the flotation guide 202, or to freelyrise and fall with the fluid level of the fluid 12 held by the container10. In one embodiment, the flotation guide 202 may be coupled to acontainer cap 206 that enables insertion of the flotation guide 202through an aperture into the container 10 and configured to seal theaperture to prevent the fluid 12 from exiting through the aperture. Inone embodiment, a magnetic field sensor may be coupled to a cap of thefluid reservoir.

Because the flotation device 202 may be constrained to movement insubstantially a single axis, the functional relationship utilized by thesensor circuitry 220 may be configured to determine a fluid level basedon a sensed magnetic strength from a single magnetic fieldsensor—although it should be understood the present disclosure,including the fluid level sensor system 200, is not limited to use of asingle magnetic field sensor. In other words, in the illustratedembodiment of FIG. 5, a plurality of magnetometer sensors may bedisposed at different positions, similar to the fluid level sensorsystem 100. The fluid level sensor system 200 may obtain and analyze thesensed magnetic field strengths from the plurality of magnetic fieldsensors to determine a fluid level.

In the illustrated embodiment, the sensor circuitry 220 may determinefluid level based on a functional relationship between (a) a position ofthe flotation device 202 that corresponds to a fluid level and (b)sensor output from the magnetic field sensor 210. For example, the fluidlevel of the fluid 12 held by the container 10 may functionallycorrespond to a measured magnetic field strength B of a single magneticfield sensor 210. With the magnetic field sensor 210 being positioned inproximity to a full level, and with the flotation device 202 beingconstrained to movement that is substantially linear or along a singleaxis, the stronger the measured magnetic field strength B, the closerthe flotation device 202 is to the magnetic field sensor 210. The weakerthe magnetic field strength B, the farther the flotation device 202 isfrom the magnetic field sensor 210. Weakening of the magnetic fieldstrength B may be indicative of the flotation device 202 may be fallingor moving away from the magnetic field sensor 210.

The flotation device 202, as discussed herein, may be configured in avariety ways. In the illustrated embodiment, the flotation device 202may include an aperture through which the flotation guide 204 may bedisposed. The flotation device 202, like the flotation device 102, mayinclude a magnetic element and a buoyant composition.

An example embodiment of a flotation device similar to the flotationdevice 202 is shown in FIG. 8, and generally designated 402. Theflotation device 402 may be similar to the flotation device 202, andincludes an aperture 403. The flotation device 402 may also includebuoyant material 409 similar to the buoyant material 109 described inconnection with the flotation device 102. The aperture 403 of theflotation device 402, when used in conjunction with a rod-type flotationguide, may allow the flotation device 402 to spin or rotate about theflotation guide. This spin or free rotation may result from sufficientclearance existing between the flotation guide and the flotation device402 such that the flotation device 402 can freely move along alongitudinal axis of the flotation guide. In one embodiment, theflotation device may interlock with a portion of the flotation guidealong the longitudinal length thereof such that free spin or rotation issubstantially prevented.

In the illustrated embodiment of FIG. 8, the flotation device 402 mayinclude a plurality of magnetic element 404, 405, 406, 407 disposedabout a center of the flotation device 402 in a manner that issubstantially uniform. In this way, as the flotation device 402 freelyspends or freely rotate about the flotation guide, a magnetic fieldstrength emanating from the plurality of magnetic element 404, 405, 406,407 may appear to be substantially the same from the perspective of themagnetometer sensor 210.

An alternative embodiment of a flotation device is shown in FIG. 7, andgenerally designated 302. The flotation device 302 may be similar to theflotation device 102, including a magnetic element 308 and buoyantcomposition 309. The distribution of the buoyant material 309 in theflotation device 302 may aid in maintaining alignment of the flotationdevice 302. For instance, in the illustrated embodiment, a principalcomponent of the buoyant composition 309 may be distributed away from acenter of the flotation device 302 (e.g., a center of mass), therebycausing first or second primary flotation surfaces 304, 306 to beoriented with respect to a surface of the fluid 12. In this way, themagnet element 308 may be aligned in a particular manner relative to asurface of the fluid 12 or the Earth. As an example, in the case of themagnetic element 308 being a permanent magnet with a N-S pole, themagnetic element 308 may be positioned within the buoyant composition309 such that the N-S pole is aligned with the surface of the fluid12—though the N-S pole may be up or down in this configuration.

Optionally, the magnetic element may be disposed on a surface of thebuoyant composition 309, as shown in broken lines in the illustratedembodiment of FIG. 7, and generally designated 308′. The magneticelement 308′ may be affixed to the buoyant composition 309 duringmanufacture, facilitating production of the buoyant composition 309separate from the magnetic element 308′.

Directional terms, such as “vertical,” “horizontal,” “top,” “bottom,”“upper,” “lower,” “inner,” “inwardly,” “outer” and “outwardly,” are usedto assist in describing the invention based on the orientation of theembodiments shown in the illustrations. The use of directional termsshould not be interpreted to limit the invention to any specificorientation(s).

The above description is that of current embodiments of the invention.Various alterations and changes can be made without departing from thespirit and broader aspects of the invention as defined in the appendedclaims, which are to be interpreted in accordance with the principles ofpatent law including the doctrine of equivalents. This disclosure ispresented for illustrative purposes and should not be interpreted as anexhaustive description of all embodiments of the invention or to limitthe scope of the claims to the specific elements illustrated ordescribed in connection with these embodiments. For example, and withoutlimitation, any individual element(s) of the described invention may bereplaced by alternative elements that provide substantially similarfunctionality or otherwise provide adequate operation. This includes,for example, presently known alternative elements, such as those thatmight be currently known to one skilled in the art, and alternativeelements that may be developed in the future, such as those that oneskilled in the art might, upon development, recognize as an alternative.Further, the disclosed embodiments include a plurality of features thatare described in concert and that might cooperatively provide acollection of benefits. The present invention is not limited to onlythose embodiments that include all of these features or that provide allof the stated benefits, except to the extent otherwise expressly setforth in the issued claims. Any reference to claim elements in thesingular, for example, using the articles “a,” “an,” “the” or “said,” isnot to be construed as limiting the element to the singular. Anyreference to claim elements as “at least one of X, Y and Z” is meant toinclude any one of X, Y or Z individually, and any combination of X, Yand Z, for example, X, Y, Z; X, Y; X, Z; and Y, Z.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A fluid sensor systemfor fluid held by a fluid reservoir system, the fluid reservoir systemhaving a cap assembly for closing an opening of fluid reservoir system,said fluid sensor system comprising: a floatation device having amagnetic element, said floatation device configured to float inproximity to a surface of the fluid in the fluid reservoir system,wherein said floatation device is buoyant with respect to the fluid; amagnetic field sensor configured to sense a magnetic field strength,said magnetic field sensor disposed on the cap assembly or a positioncorresponding to a substantially empty condition for the fluid reservoirsystem, said magnetic field sensor configured to provide a sensor outputindicative of said sensed magnetic field strength, wherein said magneticfield strength varies as a function of a position of said magneticelement with respect to said magnetic field sensor, wherein saidposition of said magnetic element corresponds to a fluid level of thefluid that is held by the fluid reservoir system; and sensor circuitryoperably coupled to said magnetic field sensor, said sensor circuitrycapable of obtaining said sensor output from said magnetic field sensor,said sensor circuitry including a processor configured to determine afluid level of the fluid based on said sensor output indicative of saidsensed magnetic field strength, said processor configured to generate anoutput signal based on said fluid level.
 2. The fluid sensor system ofclaim 1 comprising a floatation guide provided within the fluidreservoir system, wherein said floatation device is allowed to movealong a longitudinal axis of said floatation guide.
 3. The fluid sensorsystem of claim 2 wherein said floatation guide is coupled to the capassembly, and wherein said magnetic field sensor is coupled to a cap ofthe cap assembly.
 4. The fluid sensor system of claim 1 comprising aplurality of magnetic field sensors, wherein each of said plurality ofmagnetic field sensors is configured to simultaneously sense saidmagnetic field strength and generate sensor output indicative of saidsensed magnetic field strength, and wherein said processor is configuredto determine the fluid level of the fluid based on sensor output fromeach of said plurality of magnetic field sensors.
 5. The fluid sensorsystem of claim 4 wherein said plurality of magnetic field sensors aredisposed at different locations such that said magnetic field strengththat is sensed by said each magnetic field sensor of said plurality ofmagnetic field sensors is different.
 6. The fluid sensor system of claim1 wherein said processor is configured to determine said fluid levelbased on a value of said sensed magnetic field strength indicated bysaid sensor output from said magnetic field sensor.
 7. The fluid sensorsystem of claim 6 wherein said processor is configured to determine saidposition of said floatation device relative to said magnetic fieldsensor based on said value of said sensed magnetic field strengthindicated by said sensor output from said magnetic field sensor.
 8. Thefluid sensor system of claim 1 wherein said output signal is indicativeof a volume of the fluid that is held by the fluid reservoir system, andwherein said magnetic field sensor is the only sensor operable toprovide sensor output indicative of a magnetic field strength and afluid level of the fluid held by the fluid reservoir system.
 9. A fluidsensor system for fluid held by a fluid reservoir system, the fluidreservoir system having a cap assembly for closing an opening of thefluid reservoir system, said fluid sensor system comprising: afloatation device having a magnetic element, said floatation deviceconfigured to float in proximity to a surface of the fluid, wherein saidfloatation device is buoyant with respect to the fluid; a magnetic fieldsensor configured to sense a magnetic field strength, said magneticfield sensor disposed on the cap assembly or a bottom of the fluidreservoir system, said magnetic field sensor configured to providesensor output indicative of said sensed magnetic field strength, whereinsaid sensed magnetic field strength varies as a function of a positionof said magnetic element with respect to said magnetic field sensor,wherein said position of said magnetic element corresponds to a fluidlevel of the fluid that is held by the fluid reservoir system; andsensor circuitry operably coupled to said magnetic field sensor, saidsensor circuitry capable of obtaining said sensor output from saidmagnetic field sensor, said sensor circuitry including a processorconfigured to determine the fluid level of the fluid based on saidsensor output indicative of said sensed magnetic field strength.
 10. Thefluid sensor system of claim 9 comprising a floatation guide providedwithin the fluid reservoir system, wherein said floatation device isallowed to move along a longitudinal axis of said floatation guide. 11.The fluid sensor system of claim 10 wherein said floatation guide isconfigured to substantially constrain movement of said floatation deviceto a single axis of travel.
 12. The fluid sensor system of claim 11wherein said floatation guide is a rod, and wherein said floatationdevice includes an aperture through which said rod is disposed such thatsaid floatation device travels along said rod.
 13. The fluid sensorsystem of claim 9 wherein said magnetic field sensor is disposed at ornear a full level of the fluid reservoir system, and wherein saidmagnetic field sensor is coupled to a cap of the cap assembly.
 14. Thefluid sensor system of claim 9 wherein said sensor circuitry is operableto generate an output signal based on said fluid level, wherein saidoutput signal is indicative of a volume of the fluid held by the fluidreservoir system, and wherein the magnetic field sensor is the onlysensor operable to provide sensor output indicative of a magnetic fieldstrength and a fluid level of the fluid held by the fluid reservoirsystem.
 15. The fluid sensor system of claim 9 wherein said fluidreservoir system is a container formed polymeric material.
 16. The fluidsensor system of claim 9 wherein said fluid reservoir system is acontainer formed of a magnetic material.
 17. A method of determining afluid level of a fluid that is held by a fluid reservoir system, saidmethod comprising: providing a magnetic field sensor on a cap assemblyof the fluid reservoir system or a position corresponding to asubstantially empty condition for the fluid reservoir system; floating amagnetic element in proximity to a surface of the fluid, wherein aposition of the magnetic element is indicative of the fluid level;sensing, with the magnetic field sensor, a magnetic field strength,wherein the magnetic field strength varies based on the position of themagnetic element relative to the magnetic field sensor; generating, inthe magnetic field sensor, a sensor output indicating the magnetic fieldstrength; and determining the fluid level of the fluid based on thesensor output indicating the sensed magnetic field.
 18. The method ofclaim 17 comprising: sensing a secondary magnetic field strength with asecondary magnetic field sensor, wherein the magnetic field strengthvaries based on the position of the magnetic element relative to thesecondary magnetic field sensor; and sensing the magnetic field strengthand the secondary magnetic field strength at substantially the sametime.
 19. The method of claim 18 comprising processing signals outputfrom the magnetic field sensor and the secondary magnetic field sensor,wherein the signals are indicative of the sensed magnetic field strengthand the secondary magnetic field strength.
 20. The method of claim 19comprising: providing a floatation guide; and influencing, with thefloatation guide, a path of motion of the magnetic element, wherein saidinfluencing includes guiding the magnetic element to travel along alongitudinal axis of the floatation guide in response to changes in alevel of the fluid in the fluid reservoir system.